Processes for making salt systems including beryllium fluoride

ABSTRACT

Processes for producing beryllium fluoride salt systems containing beryllium fluoride, such as lithium beryllium fluoride salts, are disclosed herein. The processes include mixing ammonium beryllium fluoride with a lithium compound, melting the mixture to form a molten phase, purging the molten phase, and cooling the molten phase. This reduces the number of manufacturing steps needed to obtain the beryllium fluoride containing salt.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/052,589, filed Sep. 19, 2014, the entirety of which arefully incorporated by reference.

BACKGROUND

The present disclosure relates to processes for manufacturing saltsystems containing beryllium fluoride.

Current designs of nuclear fusion and fusion/fission reactors haveconsidered the use of liquid lithium beryllium fluoride (FLiBe) as acooling medium for various parts of the reactor. FLiBe can also be usedto breed tritium, which can be harvested in fusion reactions to make newfusion targets.

FLiBe is a salt of lithium fluoride and beryllium fluoride of varyingratios. This lithium beryllium fluoride has been used extensively in itsliquid state as a heat exchange fluid in applications such as solarenergy storage, molten salt fission reactors, and fusion reactors, aswell as in the electrochemical production of beryllium metal. The lowmelting point of beryllium fluoride and the fact that its combinationwith lithium fluoride produces a eutectic with a low melting point isvery suitable for such applications. For molten salt reactors, theoptimum molten salt is one with a low vapor pressure, low melting point,and high heat capacity, and FLiBe provides all of these characteristics.FLiBe is also being considered for use in fission reactors that usethorium as a fuel.

The traditional method of producing lithium beryllium fluoride has beenthrough the direct co-melting of lithium fluoride and beryllium fluoridein a controlled atmosphere, as shown in Reaction (1):2LiF+BeF₂→Li₂BeF₄  (1)

This reaction is slightly exothermic (ΔH at 1000° C.=−2.59 kcal/mol),but the free energy (ΔG at 1000° C.=−11.7 kcal/mol) is also slightlynegative. The log K value for this reaction is 2.01, which is very lowand indicates that the reaction does not proceed completely to formFLiBe.

It would be desirable to provide processes for obtaining lithiumberyllium fluoride salts that can be simpler and/or result in greaterconversion of reactants to product.

BRIEF DESCRIPTION

The present disclosure relates to processes for forming salt systemscontaining beryllium fluoride. Generally, ammonium beryllium fluoride isused as a reactant with other compounds. The compounds are mixed to forma reaction mixture that is then melted together. The molten phase ispurged to remove residual gases and other byproducts. The molten phaseis then cooled to obtain the salt product.

Disclosed in various embodiments here are processes for producing alithium beryllium fluoride salt, comprising: mixing ammonium berylliumfluoride with a lithium compound to form a reaction mixture; melting thereaction mixture to produce a molten phase; purging the molten phase;and cooling the molten phase to obtain the lithium beryllium fluoridesalt.

The melting can occur at a temperature of from about 100° C. to about1000° C., or from about 300° C. to about 1000° C., or from about 350° C.to about 1000° C.

The gases produced during the melting step can be withdrawn.

Sometimes, the lithium compound comprises an enriched lithium-6 compoundand a natural lithium compound.

The purging may be performed with a combination of hydrogen and hydrogenfluoride gas.

Sometimes, a sodium salt is also included in the reaction mixture, andthe resulting salt is a lithium sodium beryllium fluoride (FLiNaBe)salt.

Alternatively, a potassium salt can be included in the reaction mixture,and the resulting salt is a lithium potassium beryllium fluoride(FLiKBe) salt.

The molten phase may be poured into a mold prior to cooling.

The resulting lithium beryllium fluoride salt may contain from about 1wt % to about 99 wt % of beryllium fluoride. In some embodiments, themolar ratio of lithium fluoride to beryllium fluoride in the lithiumberyllium fluoride salt is at least 2:1.

These and other non-limiting characteristics are more particularlydescribed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings, which arepresented for the purposes of illustrating the exemplary embodimentsdisclosed herein and not for the purposes of limiting the same.

FIG. 1 is a process diagram showing a conventional method for producingFLiBe salts using lithium fluoride and beryllium fluoride.

FIG. 2 is a process diagram illustrating the processes of the presentdisclosure, which use ammonium beryllium fluoride.

FIG. 3 is a phase diagram for a lithium fluoride-beryllium fluoridesystem.

DETAILED DESCRIPTION

A more complete understanding of the components, processes, andapparatuses disclosed herein can be obtained by reference to theaccompanying drawings. These figures are merely schematicrepresentations based on convenience and the ease of demonstrating thepresent disclosure, and are, therefore, not intended to indicaterelative size and dimensions of the devices or components thereof and/orto define or limit the scope of the exemplary embodiments.

Although specific terms are used in the following description for thesake of clarity, these terms are intended to refer only to theparticular structure of the embodiments selected for illustration in thedrawings, and are not intended to define or limit the scope of thedisclosure. In the drawings and the following description below, it isto be understood that like numeric designations refer to components oflike function.

The singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise.

As used in the specification and in the claims, the term “comprising”may include the embodiments “consisting of” and “consisting essentiallyof.”

Numerical values should be understood to include numerical values whichare the same when reduced to the same number of significant figures andnumerical values which differ from the stated value by less than theexperimental error of conventional measurement technique of the typedescribed in the present application to determine the value.

All ranges disclosed herein are inclusive of the recited endpoint andindependently combinable (for example, the range of “from 2 grams to 10grams” is inclusive of the endpoints, 2 grams and 10 grams, and all theintermediate values).

As used herein, approximating language may be applied to modify anyquantitative representation that may vary without resulting in a changein the basic function to which it is related. Accordingly, a valuemodified by a term or terms, such as “about” and “substantially,” maynot be limited to the precise value specified. The modifier “about”should also be considered as disclosing the range defined by theabsolute values of the two endpoints. For example, the expression “fromabout 2 to about 4” also discloses the range “from 2 to 4.”

The processes of the present disclosure relate generally to theproduction of a lithium beryllium fluoride salt. Exemplary lithiumberyllium fluoride salts include those of the formulas Li₂BeF₄ andLiBeF₃, which can be generalized as salts of the formula nLiF—BeF₂,where n is an integer. The term “lithium beryllium fluoride salt” shouldbe construed as requiring the presence of lithium, beryllium, andfluorine at a minimum. Other salts which should be considered as fallingwithin the scope of this term include lithium sodium beryllium fluoride(FLiNaBe, a ternary mixture of LiF, BeF₂, and NaF) and lithium potassiumberyllium fluoride (FliKBe, a ternary mixture of LiF, BeF₂, and KF).

The conventional method of producing a lithium beryllium fluoride saltrequires the intermediate production of lithium fluoride, which is thenmixed and melted with beryllium fluoride. Lithium fluoride can be madein different ways. For example, lithium carbonate and hydrofluoric acidcan be converted to lithium fluoride. Alternatively, lithium carbonatecan be mixed together with ammonium fluoride and heated to 400° C. for 4hours to produce lithium fluoride. Finally, lithium carbonate can bereacted with ammonium bifluoride at high temperature to produce lithiumfluoride. Byproducts of such a reaction could include ammoniumcarbonate, ammonium bicarbonate, and possibly ammonium fluoride.

A conventional method is illustrated in FIG. 1. Here, lithium carbonateis dissolved in ammonia water and reacted with hydrofluoric acid, thenfiltered and dried to obtain lithium fluoride. The lithium fluoride isthen melted with beryllium fluoride, purified, and cooled to obtain thelithium beryllium fluoride salt. Seven steps (the square boxes) areneeded to produce the final product from the starting ingredients.

Generally, in the processes of the present disclosure, ammoniumberyllium fluoride (ABF) is used as a beryllium source. ABF has theformula (NH₄)₂BeF₄. ABF is mixed with a lithium compound to form areaction mixture. The reaction mixture is then heated to melt thecompounds and produce a molten phase. The molten phase is purged toremove residual gases and byproducts, then cooled to obtain the finallithium beryllium fluoride salt. This is shown in FIG. 2. Two examplesof the reaction of the present disclosure are provided below asReactions (2) and (3):(NH₄)₂BeF₄+2LiOH→Li₂BeF₄+2NH₃(g)+2H₂O(g)  (2)(NH₄)₂BeF₄+LiOH→LiBeF₃+NH₃(g)+H₂O(g)+NH₄F  (3)

One advantage of the processes of the present disclosure is that they donot require the intermediate steps of producing lithium fluoride andberyllium fluoride separately prior to making the Li—Be—F salt.Comparing FIG. 1 and FIG. 2, the processes of the present disclosureneed only four steps compared to the seven steps of conventionalmethods. Avoiding the need to produce beryllium fluoride reduces capitalcosts, production costs, and materials handling issues. In addition, thereactions have a negative Gibbs free energy (ΔG) and are endothermic.Reaction (2) has a ΔG at 600° C. of −111 kcal/mol and a ΔH at 600° C. of+51.1 kcal/mol. Reaction (3) has a ΔG at 600° C. of −63.3 kcal/mol and aΔH at 600° C. of +49.6 kcal/mol. It is also expected that the reactionswill obtain near complete conversion of reactant to product. Includedare appendices showing the thermodynamic values for the reactions over arange of temperatures.

Initially, the ammonium beryllium fluoride (ABF) salt is mixed with alithium compound to form a reaction mixture. The lithium compound canbe, for example, lithium hydroxide (LiOH) or lithium carbonate (Li₂CO₃).The compounds can be mixed together using known apparatuses, for examplea ball mill or a blender. If it is desired to produce FLiNaBe or FLiKBe,an appropriate sodium or potassium compound can also be mixed in withthe ABF and the lithium compound. Such compounds could include NaOH,KOH, Na₂CO₃, or K₂CO₃.

It is noted that naturally occurring lithium is composed of twoisotopes: ⁶Li and ⁷Li. The natural concentration of ⁶Li is 7.5 wt % ofthe total lithium. To produce a desired level of enrichment (i.e. with agreater proportion of ⁶Li), a natural lithium compound and an enrichedlithium-6 compound can be blended in a desired proportion in thereaction mixture to obtain the desired enrichment in the final Li—Be—Fsalt.

Next, the reaction mixture is melted to produce a molten phase. Thereaction mixture can be melted, for example, using a graphite furnace.The melting generally occurs at a temperature from about 100° C. toabout 1000° C., or in more specific embodiments from about 300° C. toabout 1000° C. or from about 350° C. to about 1000° C. In thistemperature range, the reaction is endothermic and has a negative Gibbsfree energy.

During the melting of the reaction mixture, several byproducts can beformed. As seen in Reactions (2) and (3), these can include ammoniumfluoride (NH₄F), ammonia (NH₃), water (H₂O), and/or hydrogen fluoride(HF). Gaseous byproducts can be withdrawn while the reaction mixture ismelting, for example by use of vacuum.

The molten phase is then purged. A combination of hydrogen and hydrogenfluoride gas can be injected through the molten phase to remove residualmoisture, carbon dioxide, and other entrapped gases.

The molten phase is then cooled to obtain the lithium beryllium fluoridesalt. If desired, the molten phase can be poured into a mold and thencooled. The resulting salt is a combination of lithium fluoride andberyllium fluoride, and optionally other fluoride salts. In someparticular embodiments, the molar ratio of lithium fluoride to berylliumfluoride is at least 1:1, or is at least 2:1.

The resulting lithium beryllium fluoride salt can range from about 1 wt% to about 99 wt % of the beryllium fluoride salt. In particularembodiments, the optimum composition is that which results in the lowestmelting point of the molten salt system. In the case of FLiBe, a meltingpoint below 400° C. can be achieved at approximately 50 mol % Berylliumfluoride. FIG. 3 shows the phase diagram for the berylliumfluoride-lithium fluoride system.

Again, the processes of the present disclosure avoid the preparation ofberyllium fluoride as an intermediate. Rather, the reaction of ABF withthe lithium compound results in formation of the beryllium fluoride. ABFsalts are also far more stable than beryllium fluoride, and thus usingABF reduces any handling and storage challenges that might exist withberyllium fluoride.

One of the purest forms of beryllium compounds produced industrially isammonium beryllium fluoride (ABF). Lithium can also be obtained in highpurity, so the resulting purity of the lithium beryllium fluoride saltshould also be very high.

The molten FLiBe phase could be used to produce beryllium metal as well.The molten FLiBe phase could be subjected to an applied electron currentthrough electrodes, with beryllium metal flakes being formed at thecathode and HF/F₂ gas being generated at the anode.

The present disclosure has been described with reference to exemplaryembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the present disclosure be construed asincluding all such modifications and alterations insofar as they comewithin the scope of the appended claims or the equivalents thereof.

The invention claimed is:
 1. A process for producing a lithium berylliumfluoride salt, comprising: mixing ammonium beryllium fluoride with alithium compound to form a reaction mixture; melting the reactionmixture to produce a molten phase; purging the molten phase; and coolingthe molten phase to obtain the lithium beryllium fluoride salt; whereinthe lithium compound is lithium hydroxide (LiOH) or lithium carbonate(Li₂CO₃).
 2. The process of claim 1, wherein the melting occurs at atemperature of from about 100° C. to about 1000° C.
 3. The process ofclaim 1, wherein the melting occurs at a temperature of from about 300°C. to about 1000° C.
 4. The process of claim 1, wherein the meltingoccurs at a temperature of from about 350° C. to about 1000° C.
 5. Theprocess of claim 1, wherein gases produced during the melting arewithdrawn.
 6. The process of claim 1, wherein the lithium compoundcomprises an enriched lithium-6 compound and a natural lithium compound.7. The process of claim 1, wherein the purging is performed with acombination of hydrogen and hydrogen fluoride gas.
 8. The process ofclaim 1, wherein a sodium salt is also included in the reaction mixture,and the resulting salt is a lithium sodium beryllium fluoride (FLiNaBe)salt.
 9. The process of claim 1, wherein a potassium salt is alsoincluded in the reaction mixture, and the resulting salt is a lithiumpotassium beryllium fluoride (FLiKBe) salt.
 10. The process of claim 1,wherein the molten phase is poured into a mold prior to cooling.
 11. Theprocess of claim 1, wherein the lithium beryllium fluoride salt containsfrom about 1 wt % to about 99 wt % of beryllium fluoride.
 12. Theprocess of claim 1, wherein the molar ratio of lithium fluoride toberyllium fluoride in the lithium beryllium fluoride salt is at least2:1.